McMurray's Test: Understanding a Positive Result and Meniscal Tears

What is McMurray's test positive?

A positive McMurray's test indicates a high likelihood of a meniscal tear within the knee joint, with the specific maneuver eliciting symptoms often pinpointing whether the medial or lateral meniscus is affected.

Understanding McMurray's Test

McMurray's test is a foundational orthopedic diagnostic maneuver used by healthcare professionals to assess the integrity of the menisci in the knee. Developed by Dr. Thomas Porter McMurray, it is a dynamic test that attempts to reproduce the symptoms of a meniscal tear by applying specific compressive and rotational forces to the knee joint. Its primary purpose is to identify tears in the medial or lateral meniscus, which are common knee injuries.

The Anatomy of the Meniscus

To understand McMurray's test, it's crucial to grasp the role of the menisci. The knee joint contains two C-shaped, wedge-like pieces of fibrocartilage: the medial meniscus (on the inner side of the knee) and the lateral meniscus (on the outer side). These structures serve several vital functions:

• Shock Absorption: They cushion the impact between the femur (thigh bone) and the tibia (shin bone).
• Load Distribution: They help distribute forces evenly across the knee joint.
• Joint Stability: They contribute to the overall stability of the knee.
• Lubrication: They assist in the lubrication of the joint.

Meniscal tears often occur due to twisting injuries, deep squatting, or direct impact, especially in sports that involve sudden changes in direction.

What Constitutes a "Positive" McMurray's Test?

A McMurray's test is considered "positive" when the specific maneuver performed by the examiner elicits a palpable or audible "click" or "thud," often accompanied by pain, typically felt along the joint line. The presence of pain alone, without a distinct mechanical sensation, is generally not sufficient for a positive test, as other knee pathologies can cause pain.

The test differentiates between medial and lateral meniscal tears based on the specific rotational and stress application:

• Positive for Medial Meniscus Tear: This is typically indicated when the examiner externally rotates the tibia (shin bone outwards) and then slowly extends the knee from a fully flexed position, often while applying a valgus stress (pushing the knee inwards). The "click" or pain will usually be felt on the inner (medial) side of the knee.
• Positive for Lateral Meniscus Tear: This is suggested when the examiner internally rotates the tibia (shin bone inwards) and then slowly extends the knee from a fully flexed position, often while applying a varus stress (pushing the knee outwards). The "click" or pain will typically be felt on the outer (lateral) side of the knee.

The "click" or "thud" sensation is thought to occur as the torn portion of the meniscus is caught or compressed between the femoral condyle and the tibial plateau.

How the Test is Performed (Brief Overview)

While the exact execution is for trained professionals, understanding the mechanics helps clarify the test's purpose:

1. Patient Position: The patient lies supine (on their back) with the knee fully flexed.
2. Examiner Position: The examiner holds the patient's heel with one hand and places the other hand over the knee joint, specifically palpating the joint line.
3. Maneuver Execution:
   • For the medial meniscus, the examiner externally rotates the tibia and applies a valgus stress while slowly extending the knee.
   • For the lateral meniscus, the examiner internally rotates the tibia and applies a varus stress while slowly extending the knee.
4. Observation: The examiner carefully watches for the patient's pain response and feels for any clicks, thuds, or grinding sensations.

Clinical Significance and Interpretation

A positive McMurray's test serves as a strong clinical indicator for a meniscal tear. However, it is crucial to interpret the results within the context of a comprehensive knee examination, including:

• Patient History: Details about the injury mechanism, symptoms (e.g., locking, catching, swelling, instability), and aggravating activities.
• Other Physical Exam Findings: Such as joint line tenderness, effusion (swelling), range of motion limitations, and the results of other knee stability tests.
• Imaging Studies: While highly indicative, McMurray's test is not definitive. Magnetic Resonance Imaging (MRI) is often used to confirm the diagnosis, determine the type and location of the tear, and rule out other knee pathologies.

Limitations and Considerations

Despite its utility, McMurray's test has certain limitations:

• Sensitivity and Specificity: Like all clinical tests, it is not 100% accurate. False positives (test is positive, but no tear) or false negatives (test is negative, but a tear exists) can occur.
• Acute Swelling: In cases of acute knee injury with significant swelling, the test may be less reliable or difficult to perform effectively.
• Examiner Dependence: The accuracy of the test heavily relies on the skill and experience of the examiner.
• Concomitant Injuries: Other knee injuries (e.g., ligamentous laxity) can sometimes influence the test's interpretation.
• Part of a Battery: It is rarely used in isolation; rather, it is one component of a thorough clinical assessment of the knee.

When to Seek Medical Advice

If you experience persistent knee pain, especially after a specific injury, or if you notice symptoms such as clicking, catching, locking, or a feeling of instability in your knee, it is imperative to seek professional medical advice. A healthcare professional, such as a physician, orthopedic specialist, or physical therapist, can perform a comprehensive evaluation, including McMurray's test and other diagnostic procedures, to accurately diagnose your condition and recommend the most appropriate course of treatment.